1. Field of the Invention
The present invention relates to a semiconductor switching element with a high-breakdown voltage (which will be hereinafter referred to as a “high-voltage semiconductor switching element”) including an insulated gate switching element, and more particularly relates to a high-voltage semiconductor switching element having an overcurrent protection function to protect the switching element from an overcurrent.
2. Description of the Related Art
FIGS. 18A to 18C illustrate the configuration of a typical lateral insulated gate bipolar transistor (hereinafter referred to as an “IGBT”). FIG. 18A is a plan view of the conventional lateral IGBT 100, and FIGS. 18B and 18C are cross-sectional views taken along the lines A-A′ and B-B′ in FIG. 18A, respectively. In the lateral IGBT 100 shown in FIGS. 18A to 18C, a P-type base region 102 is formed in a surface portion of an N-type semiconductor substrate 101, and an N-type emitter region 103 is formed in a surface portion of the base region 102. A gate insulating film 109 is formed on the base region 102 so as to extend from a part of the emitter region 103 to at least a part of the semiconductor substrate 101, and a gate electrode 110 is formed on the gate insulating film 109. Furthermore, a P-type collector region 107 is formed in another surface portion of the semiconductor substrate 101 so as to be spaced away from the base region 102. A collector electrode 108, which is electrically connected with the collector region 107, is formed on the surface of the collector region 107, while emitter electrodes 104, which are electrically connected with the emitter region 103 and the base region 102, are formed on the surfaces of the emitter region 103 and the base region 102.
A semiconductor device including a lateral IGBT thus configured is often used with an inductive load connected between the collector electrode of the lateral IGBT and a power supply. If a failure occurs in such a situation, the inductive load is short-circuited, causing a current more than several times a rated current to pass through the lateral IGBT. When the load is thus short-circuited, it is necessary to sense the overcurrent so as to interrupt the gate voltage or the collector voltage, because otherwise there would be a thermal breakdown in the lateral IGBT due to the temperature increase.
Therefore, in the lateral IGBT 100 shown FIGS. 18A to 18C, a sense electrode 106, which is electrically connected with the emitter region 103 and the base region 102, is formed on the surfaces of the emitter region 103 and the base region 102, each located in the predetermined area, so as to be spaced away from the emitter electrodes 104. That is, regions 111 are present between the sense electrode 106 and the emitter electrodes 104.
FIG. 19 illustrates an example of the rough circuit configuration of a semiconductor device having an overcurrent protection function for the lateral IGBT 100 shown in FIGS. 18A to 18C. In FIG. 19, the same members as those shown in FIGS. 18A to 18C are identified by the same reference numerals, and descriptions thereof will be thus omitted herein. As shown in FIG. 19, the sense electrode 106 and each emitter electrode 104 are electrically connected with each other through a sense resistor 201. In this example, an overcurrent sensing circuit 200, which is electrically connected with the sense electrode 106, is composed of a voltage comparator 202, a reference voltage circuit 203, and the aforementioned sense resistor 201, both of which are connected to the voltage comparator 202. In the semiconductor device shown in FIG. 19, a sense current 204 flows through the sense resistor 201 toward the emitter electrode 104, and a voltage generated at this time between both ends of the sense resistor 201 is compared with a voltage generated by the reference voltage circuit 203 by the voltage comparator 202. And a collector current 205 passing through the lateral IGBT 100 is controlled based on the difference between these two voltages.    [Patent Document 1] Japanese Laid-Open Publication No. 2-138773    [Patent Document 2] Japanese Laid-Open Publication No. 9-260592    [Patent Document 3] Japanese Laid-Open Publication No. 7-297387